Battlefield and tactical military communications have typically relied on field-deployed fiber optics and relatively low bandwidth radio distribution architectures to provide critical “field” communications infrastructures. While optical fiber provides broadband capabilities, it is often exposed to unintentional (and sometimes intentional) damage, limiting its operational life to a few days or hours before repair or replacement is required. Moreover, fiber is not easily deployed in mobile and frontline environments. Existing radio systems have proven robustness and mobility, but are severely lacking in bandwidth capabilities that are considered critical for modern warfare. The availability and utilization of broadband multi-channel point-to-point radio and Free Space Optical Communications (FSOC) technologies provides a means to bring fiber-like bandwidth closer to the front lines and as layered transport for broadband mobile area radios at the ground level and beyond. The bandwidth capacity of these broadband technologies provides new applications and opportunities, including enhanced communication services and the potential for enhanced communication security. The enhanced capabilities of these broadband wireless technologies is gaining the attention and consideration of various military services. Indeed, the use of FSOC and radio broadband links provides enormous benefits for military field deployments. However, the open air aspect of these technologies comes at the cost of potential interception by unintentional or hostile forces. Since these broadband links will be carrying large amounts of critical information, they clearly would be targets of interest for interception by hostile forces.
Free-space optical communication and millimeter (mm) radio systems offer two-way information transfer between remote locations without the use of wires and/or optical fibers, but each technology has transmission distance limitations associated with extreme fog, rain, smoke and dust attenuation that must be taken into consideration if optimal performance is to be expected. Hybrid FSOC/radio systems that are configured to transmit in both optical and radio frequencies (either alternately or simultaneously) have been shown to significantly reduce the attenuation effects of rain and fog and improve link performance under difficult weather conditions. Commercial versions of broadband hybrid HRL optical (FSOC) and radio wireless point-to-point systems have been in use since the late 1980's. Advanced free-space optical systems are now starting to deploy multiple optical wavelength transmission systems similar in function to the optical DWDM techniques. Based on the FCC's wireless “boundary of interest” set at 1 mm wavelength, FSOC's wavelengths and beam shaping techniques are thus not subject to licensing, spectrum interferences and the limits of shared capacity, as are the existing RF wireless technologies. Further, free-space optical communications systems may implement local area mesh network technologies for information transfer, or point-to-multipoint technology for a two-way information exchange free of government regulation or intervention.
The increasing use of free-space optical communication, as well as open-air point-to-point mm wave radio communication, for real-time government, military, and secure commercial communication applications is placing an increasing burden on methods for reducing the vulnerability of these “open” communication paths to undesired or hostile interception.
Real-time, field-transmitted data and associated data encryption keys typically have a time-dependent component after which the usefulness of the data to the desired receiver (or hostile interceptor) greatly diminishes. As such, any effective “security” method that can significantly delay (or stop) the undesired receiver's ability to derive useful data from an open-air transmission would be of interest to communities that rely on such open-air communication methods. Clearly, it is impractical and unrealistic to assume open air communications can avoid being intercepted by unwanted “motivated” recipients. Therefore, methods need to be employed that accept the reality of physical interception of the “through the air” communication by hostile recipients, while providing greatly increased complexity and time required to derive useful data from the intercepted transmission (thus, at best, recovering some portion of the information well beyond the time limit of its useful operational life).